Existing Code Division Multiple Access (CDMA)-based cellular network technologies achieve what is often referred to as downlink macro-diversity through the use of the well-known “soft handoff” mechanism. In soft handoff mechanism, multiple copies of downlink frames at the link layer or Media Access Control (MAC) sublayer are sent in parallel from a base station controller element, which is typically centrally located in the radio access network, to multiple base stations transceivers, which subsequently simultaneously transmit the downlink frame copies to the user's wireless communication device or terminal. The wireless terminal then uses techniques such as frame selection or soft combining, as well as automatic repeat request (ARQ) mechanisms in an attempt to reconstruct and correctly receive the frames sent from the base station controller. This design has evolved primarily in support of circuit-switch applications, e.g., voice, and is not well-suited for packet-switched networking/internetworking. The concentration of information through the controlling element reduces network scalability and also increases the reliability requirements, and cost, of the controlling element. The design also imposes timing, synchronization, and communication latency requirements between the base station transceivers and/or between the base station transceivers and the controlling element.
These requirements are overly restrictive for many packet-switched network/internetwork technologies. In connectionless, packet-switched networks/internetworks such as those based on the Internet Protocol (IP), a sequence of packets (or packet flow) sent from a source node to a destination node need not follow the same path throughout the network/internetwork. It is also generally desirable to confine the dynamics of a specific air-link interface technology to the interface itself, thereby allowing network layer intelligence to be brought forward to the edge of the fixed infrastructure.
Internet Protocol Overview
IP technology is designed to enable packet-switched interconnection of a heterogeneous set of computer communication networks. A potentially diverse set of network and link layer technologies are interconnected through gateways (or routers) that provide a packet forwarding service. Information is transferred from sources to destinations as blocks of data called datagrams, where sources and destinations (or hosts) are identified by fixed length addresses. Routing in IP internetworks is connectionless in nature, in that datagrams are forwarded between routers on a hop-by-hop basis using the destination address in the datagram. Each router makes an independent next-hop forwarding decision using its own internal forwarding table. IP also provides for fragmentation and reassembly of long datagrams, if necessary, for transmission through “small packet” networks. In some IP internetworks there is relatively little distinction between hosts and routers. Herein, when no distinction is required the term “node” will be used. One distinction that generally holds true is that while any IP node may send and receive datagrams, only routers forward datagrams.
IP Internetworking over Wireless Communication and Networking Technologies
Connectivity between nodes in an IP internetwork can be provided by both wired and wireless communications and network technologies. Wireless communication and network technology can be used to provide connectivity either directly between IP nodes that have wireless communication device interfaces or through non-IP wireless link-layer devices, such as a wireless access point serving as a bridge between a wireless LAN and a hardwired LAN. In any case, channel conditions, spatial relationships, and other factors have a significant impact on physical and link layer connectivity, which makes these connections more dynamic and time varying than in hardwired networks.
Before packets, e.g., IP datagrams, can be transmitted between two wireless communication devices, a viable communication connection must be established. The process of establishing a wireless communication connection may progress through a series of possible stages as follows.                1. In the first stage, which may be referred to as “physical layer synchronization”, devices typically detect one another based on physical layer mechanisms and synchronize with one another to allow further communication.        2. In the second stage, which may be referred to as “physical layer access exchange”, the devices typically exchange a series of physical layer signals or control messages to enable access to air-link resources. After this stage, the devices can send and receive link layer control messages.        3. In the third stage, which may be referred to as “link layer exchange”, the devices typically exchange a series of link layer control messages. This may include tasks such as authentication, authorization, registration and establishment of keys for enciphering and deciphering link traffic. After this stage, the devices can send and receive link layer data messages. Thus, the connection is capable of supporting the exchange of network and higher layer control and data packets (e.g., IP datagrams).        4. In the fourth stage, which may be referred to as “network layer exchange”, the devices typically exchange network and higher layer control messages. This may include tasks such as address resolution, network layer admission control, internetwork routing, and negotiating quality of service. Depending on the specifics of the network/internetwork scenario, various control traffic exchanges in this fourth stage may be required before exchange of general IP data traffic is supported (particularly data traffic that must traverse more than one network hop).        
Note that some of the message exchanges may directly or indirectly involve entities such as Authentication, Authorization and Accounting (AAA) servers other than the wireless communication devices and the entities that encompass them (particularly in the third and fourth stages above).
In some instances a communication connection may be more specifically described as either a physical-layer connection or a link-layer connection. While the specific attributes and differences may vary depending on the particular communication technology and/or protocols, the former loosely corresponds with the end of the second stage and the later with the end of the third stage. Since a link-layer connection is typically associated with link-layer functions such as message framing and ARQ, which need not be closely coupled to a particular physical layer connection, it is possible that in some communication systems a link-layer connection may include, or operate over, multiple physical layer connections. When higher layer packets are transmitted over a physical-layer or link-layer connection, they are typically partitioned into one or more frames, where each frame may include some additional header information. Depending on the underlying technology and/or protocols, frames may be either fixed or variable in length.